Diabetes is a chronic disorder affecting carbohydrate, fat and protein metabolism in animals.
Type I diabetes mellitus, which comprises approximately 10% of all diabetes cases, was previously referred to as insulin-dependent diabetes mellitus (IDDM) or juvenile onset diabetes. This disease is characterized by a progressive loss of insulin secretory function by beta cells of the pancreas. This characteristic is also shared by non-idiopathic, or “secondary”, diabetes having its origins in pancreatic disease. Type I diabetes mellitus is associated with the following clinical signs or symptoms: persistently elevated plasma glucose concentration or hyperglycemia; polyuria; polydipsia and/or hyperphagia; chronic microvascular complications such as retinopathy, nephropathy and neuropathy; and macrovascular complications such as hyperlipidemia and hypertension which can lead to blindness, end-stage renal disease, limb amputation and myocardial infarction. Therapy for IDDM patients has consistently focused on administration of exogenous insulin, which may be derived from various sources (e.g., human, bovine, porcine insulin). The use of heterologous species material gives rise to formation of anti-insulin antibodies which have activity limiting effects and result in progressive requirements for larger doses in order to achieve desired hypoglycemic effects.
Type II diabetes mellitus (non-insulin-dependent diabetes mellitus or NIDDM) is a metabolic disorder involving the dysregulation of glucose metabolism and impaired insulin sensitivity. Type II diabetes mellitus usually develops in adulthood and is associated with the body's inability to utilize or make sufficient insulin. In addition to the insulin resistance observed in the target tissues, patients suffering from type II diabetes mellitus have a relative insulin deficiency—that is, patients have lower than predicted insulin levels for a given plasma glucose concentration. Type II diabetes mellitus is characterized by the following clinical signs or symptoms: persistently elevated plasma glucose concentration or hyperglycemia; polyuria; polydipsia and/or hyperphagia; chronic microvascular complications such as retinopathy, nephropathy and neuropathy; and macrovascular complications such as hyperlipidemia and hypertension which can lead to blindness, end-stage renal disease, limb amputation and myocardial infarction. Typical treatment of Type II diabetes mellitus focuses on maintaining the blood glucose level as near to normal as possible with lifestyle modification relating to diet and exercise, and when necessary, the treatment with antidiabetic agents, insulin or a combination thereof. NIDDM that cannot be controlled by dietary management is treated with oral antidiabetic agents.
Syndrome X, also termed Insulin Resistance Syndrome (IRS), Metabolic Syndrome, or Metabolic Syndrome X, is recognized in some 2% of diagnostic coronary catheterizations. Often disabling, it presents symptoms or risk factors for the development of Type II diabetes mellitus and cardiovascular disease, including impaired glucose tolerance (IGT), impaired fasting glucose (IFG), hyperinsulinemia, insulin resistance, dyslipidemia (e.g., high triglycerides, low HDL), hypertension and obesity. Although insulin resistance is not always treated in all Syndrome X patients, those who exhibit a prediabetic state (e.g., IGT, IFG), where fasting glucose levels may be higher than normal but not at the diabetes diagnostic criterion, is treated in some countries (e.g., Germany) with metformin to prevent diabetes. The anti-diabetic agents may be combined with pharmacological agents for the treatment of the concomitant co-morbidities (e.g., antihypertensives for hypertension, hypolipidemic agents for lipidemia).
Hyperglycemia is one common characteristic of these diabetic disorders. Treatments of hyperglycemia are focused on excretion of excessive glucose directly into urine, which involves sodium-glucose cotransporters (SGLTs), primarily found in the chorionic membrane of the intestine and kidney. In particular, renal reabsorption of glucose is mediated by SGLT1 and SGLT2 (Silverman et al., 1992; Deetjen et al., 1995). SGLT1, a high-affinity low-capacity transporter with a Na+:glucose transport ratio of 2:1, is present in intestinal and renal epithelial cells (Lee et al., 1994). On the other hand, SGLT2, also known as SAAT1, a low-affinity high-capacity transporter with a Na+:glucose transport ratio of 1:1, is found in the epithelium of the kidney (You et al., 1995, MacKenzie et al., 1994). In addition, glucose absorption in the intestine is primarily mediated by SGLT1 and SGLT2. Thus, inhibition of SGLT1 and SGLT2 reduces plasma glucose through suppression of glucose reabsorption in the kidney, which was demonstrated in rodent models of IDDM and NIDDM by increasing the excretion of glucose in urine and lowering blood glucose levels.
However, there still remains a need for SGLT inhibitor compounds that have pharmacokinetic and pharmacodynamic properties suitable for use as human pharmaceuticals.